Battery and method of manufacturing battery

ABSTRACT

A welding step involves solid-state welding together an external terminal and a seat portion of an internal terminal by causing the external terminal or the internal terminal to vibrate while detaching an insulator from the external terminal in at least a region surrounding the seat portion and pressing the external terminal against the seat portion.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 16/289,856, filed Mar. 1, 2019, which claims priority from Japanese Patent Application No. 2018-037946 filed on Mar. 2, 2018, the entire contents of which are incorporated herein by reference including the specification, claims, drawings, and abstract.

BACKGROUND

The present disclosure relates to a battery and a method of manufacturing a battery.

JP 2014-11073 A discloses the following technique. A shaft portion of an internal terminal that penetrates through a battery case and an external terminal is riveted to the external terminal, and thereafter, the outer peripheral edge of the riveted portion is laser-welded to the external terminal. JP 2017-84585 A discloses that a bead portion is provided on the outer peripheral edge of the riveted portion by laser welding.

SUMMARY

A welded portion of the internal terminal and the external terminal tends to show lower electrical resistance than other contact parts between the internal terminal and the external terminal. Accordingly, the welded portion may be a primary conductive path between the internal terminal and the external terminal. When the welded portion is located at the outer peripheral edge of the riveted portion, it is possible that, for example, extraneous matters or the like may make contact with the welded portion. Because it is desired to maintain the quality of the conductive path between the internal terminal and the external terminal at high level, it is desired to prevent the welded portion between the internal terminal and the external terminal from making contact with such extraneous matters. In addition, to join the internal terminal and the external terminal by laser welding, relatively high-cost equipment, such as a laser welding machine, is necessary. Accordingly, it is proposed herein to provide a battery that has a totally novel structure and a method of manufacturing the battery.

According to this disclosure, an embodiment of the method of manufacturing a battery includes a step of preparing a battery case component, a step of preparing a gasket, a step of preparing an internal terminal, a step of preparing an insulator, a step of preparing an external terminal, an assembling step, and a welding step.

The battery case component includes a mounting hole. The gasket includes a tubular portion attachable to the mounting hole. The internal terminal includes a seat portion attachable to the tubular portion. The insulator includes a first through hole attachable to the tubular portion. The external terminal is to be disposed on the insulator, and includes a portion that overlaps the seat portion. In the assembling step, the internal terminal, the gasket, the battery case component, the insulator, and the external terminal are assembled together. In the assembling step, the tubular portion of the gasket is fitted to the mounting hole of the battery case component, the seat portion of the internal terminal is fitted to the tubular portion of the gasket, the insulator is disposed on an outer surface of the battery case component, and the external terminal is disposed on the insulator so as to overlap the seat portion. In the welding step, the seat portion and the external terminal are solid-state welded together by causing the external terminal or the internal terminal to vibrate while detaching the insulator from the external terminal in at least a region surrounding the seat portion and pressing the external terminal against the seat portion of the internal terminal. This method makes it possible to obtain consistency in the quality of solid-state welding between the external terminal and the seat portion of the internal terminal.

For example, the external terminal may include a second through hole formed in a vicinity of a portion of the external terminal that overlaps the seat portion. In this case, in the welding step, the insulator may be pressed down through the second through hole to detach the insulator from the external terminal.

The external terminal may include a second through hole formed in a vicinity of the portion of the external terminal that overlaps the seat portion, and the insulator may include a protrusion protruding into the second through hole. In this case, in the assembling step, the protrusion of the insulator may be inserted into the second through hole formed in the vicinity of the portion of the external terminal that overlaps the seat portion. Also, in the welding step, the protrusion may be pressed down to detach the insulator from the external terminal in the region surrounding the seat portion.

The protrusion may protrude from the second through hole with the external terminal being pressed against the seat portion of the internal terminal.

The external terminal may include a thinned portion having a reduced thickness and provided in a vicinity of the portion of the external terminal that overlaps the seat portion. In this case, in the welding step, the thinned portion may be pressed down to detach the insulator from the external terminal in the region surrounding the seat portion.

It is also possible that the internal terminal prepared in the step of preparing an internal terminal may include a shaft portion rising from the seat portion, and that the external terminal prepared in the step of preparing an external terminal may include an insertion hole through which the shaft portion is inserted. In this case, in the assembling step, the external terminal may be disposed on the insulator so that the shaft portion is inserted through the insertion hole. The method may further include, after or during the welding step, the step of fastening the shaft portion to a region around the insertion hole. After the fastening step, the insulator may no longer be detached from the external terminal in at least the region surrounding the seat portion.

In the welding step, ultrasonic vibrations may be applied to the internal terminal or the external terminal while clamping the internal terminal and the external terminal with a horn and an anvil, and pressing the external terminal and the seat portion of the internal terminal against each other.

In an embodiment disclosed herein, a battery includes a battery case component including a mounting hole, an internal terminal, an external terminal, and an insulating member interposed between the battery case component and the external terminal and between the battery case component and the internal terminal. The internal terminal includes a base portion and a seat portion protruding from the base portion. The base portion is overlapped on an inside of the battery case component with the insulating member being interposed between the base portion and the inside of the battery case component. The seat portion is inserted through the mounting hole with the insulating member being interposed between the seat portion and the mounting hole, and is attached to the battery case component. The external terminal includes a welded portion and a through hole. The welded portion is overlapped on the seat portion inserted through the mounting hole and is welded to the internal terminal. The through hole is formed in a vicinity of a portion of the external terminal that overlaps the seat portion. The insulating member includes a protrusion protruding into the through hole.

In an embodiment disclosed herein, a battery includes a battery case component including a mounting hole, an internal terminal, an external terminal, and an insulating member interposed between the battery case component and the external terminal and between the battery case component and the internal terminal. The internal terminal includes a base portion and a seat portion protruding from the base portion. The base portion is overlapped on an inside of the battery case component with the insulating member being interposed between the base portion and the inside of the battery case component. The seat portion is inserted through the mounting hole with the insulating member being interposed between the seat portion and the mounting hole, and is attached to the battery case component. The external terminal includes a welded portion and a thinned portion. The welded portion is overlapped on the seat portion inserted through the mounting hole and is welded to the internal terminal. The thinned portion has a reduced thickness, and is provided in a vicinity of a portion of the external terminal that overlaps the seat portion.

The internal terminal may further include a shaft portion rising from the seat portion, and the external terminal may further include an insertion hole through which the shaft portion is inserted. In this case, the shaft portion may be inserted through the insertion hole and fastened to a region around the insertion hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a sealed battery 10 according to one embodiment of the present disclosure.

FIG. 2 is a cross-sectional view illustrating a portion where an external terminal 14 and an internal terminal 15 are fitted to a battery case 11.

FIG. 3 is a cross-sectional view illustrating the internal terminal 15, a gasket 12, a lid 11 b, an insulator 13, and the external terminal 14 that are assembled together in an assembling step.

FIG. 4 is a plan view illustrating a region surrounding an insertion hole 14 c of the external terminal 14 in the assembling step.

FIG. 5 is a cross-sectional view illustrating how the external terminal 14 is pressed against a seat portion 15 c of the internal terminal 15 in a welding step.

FIG. 6 is a partial cross-sectional view taken along line VI-VI in FIG. 5 .

FIG. 7 is a cross-sectional view illustrating a fastening step.

FIG. 8 is a cross-sectional view illustrating a battery according to another embodiment of the disclosure.

FIG. 9 is a cross-sectional view illustrating a battery according to still another embodiment of the disclosure.

FIG. 10 is a cross-sectional view illustrating a battery according to yet another embodiment of the disclosure.

FIG. 11 is a cross-sectional view illustrating a battery according to further another embodiment of the disclosure.

FIG. 12 is a plan view of the internal terminal 15, illustrating how the insulator 13 is fitted to the seat portion 15 c of the internal terminal 15 in the assembling step of the battery according to the embodiment shown in FIG. 11 .

FIG. 13 is a cross-sectional view illustrating another embodiment of the battery according to the present disclosure.

DETAILED DESCRIPTION

Hereinbelow, embodiments of a battery and a method of manufacturing the battery according to the present disclosure will be described in detail. It should be noted, however, that the embodiments described herein are, of course, not intended to limit the present invention. The present invention is not limited to the embodiments described herein unless specifically stated otherwise. The drawings are depicted schematically and do not necessarily reflect actual objects. The features and components that exhibit the same effects are denoted by the same reference symbols as appropriate, and the description thereof will not be repeated. Arrows designated as U, D, L R, F, and Rr in the drawings represent respective directions, up, down, left, right, front, and rear.

Here, embodiments of a battery and a method of manufacturing the battery are described using a sealed battery 10 shown in FIGS. 1 and 2 as an example.

FIG. 1 is a partial cross-sectional view of a sealed battery 10 according to one embodiment of the present disclosure. FIG. 1 depicts the interior of the sealed battery 10 that is exposed along one wide side surface of a battery case 11 in substantially a rectangular parallelepiped shape. FIG. 2 is a cross-sectional view illustrating a portion where an external terminal 14 and an internal terminal 15 are fitted to a battery case 11. As illustrated in FIGS. 1 and 2 , the sealed battery 10 includes the battery case 11, a gasket 12, an insulator 13, the external terminal 14, the internal terminal 15, a connecting terminal 16, and an electrode assembly 20.

The electrode assembly 20 is covered with an insulating film (not shown) and is enclosed in the battery case 11. The electrode assembly 20 includes a positive electrode sheet 21 serving as a positive electrode element, a negative electrode sheet 22 serving as a negative electrode element, and separator sheets 31 and 32 each serving as a separator. Each of the positive electrode sheet 21, the first separator sheet 31, the negative electrode sheet 22, and the second separator sheet 32 is a long strip-shaped member.

The positive electrode sheet 21 includes a positive electrode current collector foil 21 a (for example, an aluminum foil) having a predetermined width and a predetermined thickness, a positive electrode active material layer 21 b containing a positive electrode active material, and an uncoated portion 21 a 1 defined along one lateral edge of the positive electrode current collector foil 21 a with a constant width. The positive electrode active material layer 21 b is formed on both faces of the positive electrode current collector foil 21 a, except for the uncoated portion 21 a 1. In a lithium-ion secondary battery, the positive electrode active material is a material that releases lithium ions during charge and absorbs lithium ions during discharge, such as lithium-transition metal composite material. Generally, other than the lithium-transition metal composite material, various materials have been proposed for use as the positive electrode active material, and the positive electrode active material is not limited to a particular material.

The negative electrode sheet 22 includes a negative electrode current collector foil 22 a (copper foil herein) having a predetermined width and a predetermined thickness, a negative electrode active material layer 22 b containing a negative electrode active material, and an uncoated portion 22 a 1 defined along one lateral edge of the negative electrode current collector foil 22 a with a constant width. The negative electrode active material layer 22 b is formed on both faces of the negative electrode current collector foil 22 a, except for the uncoated portion 22 a 1. In a lithium-ion secondary battery, for example, the negative electrode active material is a material that absorbs lithium ions during charge and releases the absorbed lithium ions during discharge, such as graphite. Generally, other than graphite, various materials have been proposed for use as the negative electrode active material, and the negative electrode active material is not limited to a particular material.

Each of the separator sheets 31 and 32 may be formed of, for example, an electrolyte permeable porous resin sheet with required heat resistance. Various proposals have been made about the separator sheets 31 and 32, and there is no particular restriction on the separator sheets 31 and 32.

Here, the negative electrode active material layer 22 b is formed, for example, so as to be wider than the positive electrode active material layer 21 b. The width of the separator sheets 31 and 32 is wider than the width of the negative electrode active material layer 22 b. The uncoated portion 21 a 1 of the positive electrode current collector foil 21 a and the uncoated portion 22 a 1 of the negative electrode current collector foil 22 a are arranged at laterally opposite ends. The positive electrode sheet 21, the first separator sheet 31, the negative electrode sheet 22, and the second separator sheet 32 are aligned longitudinally, stacked one on another, and wound together. The negative electrode active material layer 22 b covers the positive electrode active material layer 21 b with the separator sheets 31 and 32 interposed therebetween. The negative electrode active material layer 22 b is covered with the separator sheets 31 and 32. The uncoated portion 21 a 1 of the positive electrode current collector foil 21 a protrudes from one of the lateral edges of the separator sheets 31 and 32. The uncoated portion 22 a 1 of the negative electrode current collector foil 22 a protrudes from the other one of the lateral edges of the separator sheets 31 and 32.

As illustrated in FIG. 1 , the electrode assembly 20 is formed in a flattened shape along one plane containing the winding axis so that it can be enclosed in a case main body 11 a of the battery case 11. Along the winding axis of the electrode assembly 20, the uncoated portion 21 a 1 of the positive electrode current collector foil 21 a is disposed at one end, and the uncoated portion 22 a 1 of the negative electrode current collector foil 22 a is disposed at the opposite end. The uncoated portion 21 a 1 of the positive electrode current collector foil 21 a and the uncoated portion 22 a 1 of the negative electrode current collector foil 22 a are attached to respective internal terminals 15, which are respectively attached to opposite longitudinal end portions of a lid 11 b. The electrode assembly 20 is attached to the internal terminals 15, which are attached to the lid 11 b, in this manner, and is enclosed in the battery case 11.

The battery case 11 has a flat prismatic housing region. The battery case 11 includes the case main body 11 a and the lid 11 b. The battery case may be made of aluminum or aluminum alloy, such as 1000 series aluminum alloy or 3000 series aluminum alloy. In this embodiment, the case main body 11 a has a substantially flat rectangular parallelepiped shape, and it has an opening in one face thereof that has longer sides and shorter sides. The lid 11 b is a plate-shaped member that has a shape corresponding to the opening of the case main body 11 a so as to be fitted to the opening. At opposite longitudinal end portions of the lid 11 b, mounting holes 11 c (see FIG. 2 ) are formed for mounting the external terminals 14 and the internal terminals 15. In this embodiment, a protrusion 11 c 1 protruding inward of the lid 11 b is provided at the rim of the mounting hole 11 c.

As illustrated in FIG. 2 , the battery disclosed herein includes a battery case component (the lid 11 b in this embodiment), an internal terminal 15, an external terminal 14, and an insulating member (12, 13). Here, the insulating member is interposed between the lid 11 b and the internal terminal 15 and between the lid 11 b and the external terminal 14, the lid 11 b serving as the battery case component. In this embodiment, the insulating member includes a gasket 12 and an insulator 13.

Herein, as illustrated in FIGS. 1 and 2 , the internal terminal 15 includes a lead portion 15 a, a base portion 15 b, a seat portion 15 c, and a shaft portion 15 d.

As illustrated in FIGS. 1 and 2 , the base portion 15 b is a portion of the internal terminal 15 that is lapped over the gasket 12 inside the lid 11 b. The base portion 15 b is attached to the lid 11 b with the gasket 12 interposed between the base portion 15 b and the lid 11 b. The lead portion 15 a is a portion of the internal terminal 15 that extends from the base portion 15 b toward the inside of the battery case 11. Referring to FIG. 1 , the lead portion 15 a of the internal terminal 15 that is on the left side is welded to the uncoated portion 21 a 1 of the positive electrode current collector foil 21 a of the electrode assembly 20. The lead portion 15 a of the internal terminal 15 that is on the right side is welded to the uncoated portion 22 a 1 of the negative electrode current collector foil 22 a of the electrode assembly 20. The seat portion 15 c protrudes from the base portion 15 b. The seat portion 15 c is inserted through the mounting hole 11 c of the lid 11 b and fitted to the lid 11 b, with the gasket 12 interposed between them. The shaft portion 15 d rises from a central part of the seat portion 15 c. Herein, the rising portion of the shaft portion 15 d (that is, the central part of the base portion 15 c) may not necessarily be at the absolute center of the seat portion 15 c. The shaft portion 15 d may be off the center of the seat portion 15 c.

The gasket 12 is interposed between the internal terminal 15 and the mounting hole 11 c of the lid 11 b. The gasket 12 guarantees sufficient sealing performance of the mounting hole 11 c of the lid 11 b and also provides electrical insulation between the lid 11 b and the internal terminal 15. The gasket 12 is composed of a resin member having desired elasticity. An example of material usable for the gasket 12 is tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (also referred to as PFA).

In this embodiment, the gasket 12 includes a tubular portion 12 a, a flange portion 12 b, a surrounding portion 12 c, and a retaining portion 12 d. The tubular portion 12 a is a portion of the gasket 12 that protrudes from the flange portion 12 b. The seat portion 15 c and the shaft portion 15 d of the internal terminal 15 are inserted through the tubular portion 12 a. The tubular portion 12 a is fitted to the inner circumferential surface of the mounting hole 11 c of the lid 11 b. The tubular portion 12 a is has an inner diameter that is substantially the same size as the outer diameter of the seat portion 15 c of the internal terminal 15 and also has an outer diameter that is substantially the same size as the inner diameter of the mounting hole 11 c. The flange portion 12 b extends radially from one end of the tubular portion 12 a. The flange portion 12 b is a plate-shaped member that is to be fitted to the inner side surface of the lid 11 b. The surrounding portion 12 c extends from the peripheral edge of the flange portion 12 b opposite the tubular portion 12 a. The retaining portion 12 d is provided to be the lower surface of the gasket 12. The retaining portion 12 d includes a recess that corresponds to the shape of the base portion 15 b of the internal terminal 15, which will be detailed later. The retaining portion 12 d is a portion of the gasket 12 on which the base portion 15 b is positioned.

As illustrated in FIG. 2 , the gasket 12 is fitted to the seat portion 15 c of the internal terminal 15 and is mounted into the mounting hole 11 c of the lid 11 b. In this case, the seat portion 15 c protrudes from the mounting hole 11 c of the lid 11 b, and the insulator 13 is fitted thereto outside the lid 11 b. The height of the seat portion 15 c of the internal terminal 15 is adjusted so that the seat portion 15 c protrudes from the lid 11 b by a dimension corresponding to the thickness of the insulator 13, under the condition that the tubular portion 12 a of the gasket 12 is fitted to the seat portion 15 c and also the seat portion 15 c is fitted in the mounting hole 11 c of the lid 11 b. The seat portion 15 c is fitted into the mounting hole 11 c of the lid 11 b with the tubular portion 12 a of the gasket 12 being attached to the seat portion 15 c. The shaft portion 15 d of the internal terminal 15 rises from a central part of the seat portion 15 c. The tip end 15 d 1 of the shaft portion 15 d of the internal terminal 15 is crushed and fastened to the outside of the external terminal 14 in a region around the insertion hole 14 c. Note that FIG. 2 depicts the shaft portion 15 d of the internal terminal 15 that has been crushed and fastened. The shaft portion 15 d of the internal terminal 15 that has not yet been fastened is in a substantially columnar shape (see FIG. 3 ).

The insulator 13 is a member that is disposed on an outside of the lid 11 b to provide electrical insulation between the lid 11 b and the external terminal 14 as well as between the lid 11 b and the connecting terminal 16. The insulator 13 is composed of a resin member. Examples of materials usable for the insulator 13 include polypropylene (also referred to as PP), polypropylene (also referred to as PE), and polyphenylene sulfide (also referred to as PPS).

In this embodiment, the lower surface of the insulator 13 is provided with a protruding portion 13 a, as illustrated in FIG. 2 . The protruding portion 13 a is fitted into a recess 11 b 1 of the lid 11 b. The upper surface of the insulator 13 is provided with a recess 13 b, in which the connecting terminal 16 is to be disposed, and a recess 13 c, in which the external terminal 14 is to be fitted. In the recess 13 c, in which the external terminal 14 is fitted, a through hole 13 d is formed at a position that corresponds to the mounting hole 11 c formed in the lid 11 b. The through hole 13 d has substantially the same shape as that of the seat portion 15 c so that the seat portion 15 c of the internal terminal 15 can be inserted therethrough. The through hole 13 d is attached to the seat portion 15 c of the internal terminal 15, which protrudes from the mounting hole 11 c of the lid 11 b, and the insulator 13 is fitted so as to cover the lid 11 b. In the upper surface of the insulator 13, protrusions 13 e are provided in a region surrounding the through hole 13 d. Each of the protrusions 13 e is a part that is to be fitted to a through hole 14 e of the external terminal 14. Herein, the through hole 13 d of the insulator 13 is referred to as a “first through hole” when appropriate, in order to distinguish the through hole 13 d from the through hole 14 e of the external terminal 14. The through hole 14 e of the external terminal 14 is referred to as a “second through hole” when appropriate, in order to distinguish the through hole 14 e from the through hole 13 d of the insulator 13.

The external terminal 14 and the connecting terminal 16 are fitted to the outside of the lid 11 b with the insulator 13 interposed therebetween. As illustrated in FIG. 2 , the outer surface of the lid 11 b is formed with a recess 11 b 1 that is recessed corresponding to the location at which the connecting terminal 16 is to be fitted. The external terminal 14, the internal terminal 15, and the connecting terminal 16 may be made of materials that can withstand the potentials respectively required for the positive electrode side and the negative electrode side. For example, for the positive electrode side, it is possible to use aluminum or aluminum alloys, such as 1000 series aluminum alloys, 3000 series aluminum alloys, and 6000 series aluminum alloys. For the negative electrode side, it is possible to use copper or copper alloys, such as 1000 series copper alloys.

The external terminal 14 includes a welded portion 14 d and a through hole 14 e. Here, the welded portion 14 d is a portion of the external terminal 14 that is welded to the internal terminal 15, which is within a portion of the external terminal 14 that overlaps the seat portion 15 c of the internal terminal 15 that is inserted through the mounting hole 11 c of the lid 11 c. The through hole 14 e is formed in a vicinity of the portion of the external terminal 14 that overlaps the seat portion 15 c. A protrusion 13 e protruding from the upper surface of the insulator 13 serving as an insulating member is fitted into the through hole 14 e. In this embodiment, the protrusion 13 e has a required height such that the protrusion 13 e can protrude from the through hole 14 e, with the external terminal 14 being pressed against the seat portion 15 c of the internal terminal 15.

In this embodiment, as illustrated in FIG. 2 , the external terminal 14 is overlapped on the outside of the lid 11 b with the insulator 13 interposed between the external terminal 14 and the lid 11 b. In this embodiment, the external terminal 14 includes an insertion hole 14 c through which the shaft portion 15 d of the internal terminal 15 is inserted. A region around the insertion hole 14 c overlaps the seat portion 15 c. The external terminal 14 and the internal terminal 15 are welded to each other in a portion of the external terminal 14 that overlaps the seat portion 15 c of the internal terminal 15. Although it is possible to weld all around the portion of the external terminal 14 that overlaps the seat portion 15 c, it is preferable to weld at least a portion of the circumferential portion of the external terminal 14 that overlaps the seat portion 15 c. Herein, within the portion that overlaps the seat portion 15 c in a region around the insertion hole 14 c, the portion where the external terminal 14 and the internal terminal 15 are welded together is referred to as a welded portion 14 d. The welded portion 14 d provides reliable electrical conduction between the external terminal 14 and the tip end 15 d 1 of the internal terminal 15.

The through hole 14 e is formed in the external terminal 14 within the vicinity of the portion where the external terminal 14 is overlapped on the seat portion 15 c. In this embodiment, the through hole 14 e is formed at a position slightly away radially outward of the insertion hole 14 c from the portion where the external terminal 14 is overlapped on the seat portion 15 c, along the longitudinal axis of the lid 11 b. In this embodiment, two through holes 14 e are formed along the longitudinal axis of the lid 11 b at respective two locations that sandwich the portion where the external terminal 14 is overlapped on the seat portion 15 c. Formed between the through holes 14 e is the insertion hole 14 c, through which the shaft portion 15 d of the internal terminal 15 is to be inserted.

The external terminal 14 is disposed on the insulator 13, which is disposed on the outside of the lid 11 b. The external terminal 14 also retains the connecting terminal 16. The external terminal 14 is a plate-shaped member disposed along the longitudinal axis of the lid 11 b. A step 14 a is provided at a longitudinal central portion of the external terminal 14. An attachment hole 14 b, which is to be attached to a shaft portion 16 b of the connecting terminal 16, is formed at one side of the step 14 a. The insertion hole 14 c, through which the shaft portion 15 d of the internal terminal 15 is to be inserted, is formed at the opposite side.

The connecting terminal 16 includes a flange portion 16 a and a shaft portion 16 b. The flange portion 16 a is positioned and fitted into the recess 13 b provided in the insulator 13, which is disposed on the outside of the lid 11 b. Accordingly, the flange portion 16 a and the recess 13 b may desirably have corresponding shapes. The shaft portion 16 b serves as an output terminal. For example, when a battery pack is constructed, a bus bar is attached to the shaft portion 16 b. In the step of fitting the external terminal 14, the external terminal 14 is fitted onto the insulator 13. In this embodiment, the shaft portion 16 b of the connecting terminal 16, which is disposed on the insulator 13, is passed through the attachment hole 14 b of the external terminal 14. Then, the shaft portion 15 d of the internal terminal 15, which is exposed above the insulator 13, is passed through the insertion hole 14 c of the external terminal 14. Furthermore, the external terminal 14 is fitted on top of the insulator 13.

In this embodiment, after assembling the various parts as described above, the seat portion 15 c of the internal terminal 15 and the overlapping portion of the external terminal 14 are welded together. Further, the tip end 15 d 1 of the shaft portion 15 d of the internal terminal 15 is fastened to the external terminal 14.

In the battery disclosed herein, the internal terminal 15 and the external terminal 14 that are fitted onto the lid 11 b, serving as the battery case component, are pressed so that they are clamped together while interposing the gasket 12 and the insulator 13 between the internal terminal 15 and the lid 11 b and between the external terminal 14 and the lid 11 b, and also the shaft portion 15 d of the internal terminal 15 is deformed. That is, the tip end 15 d 1 of the shaft portion 15 d of the internal terminal 15 is deformed and fastened to the external terminal 14. Thereby, the internal terminal 15, the gasket 12, the insulator 13, and the external terminal 14 are secured to the lid 11 b of the battery case 11.

Thus, as illustrated in FIG. 2 , the internal terminal 15 of the battery 10 includes the base portion 15 b, the seat portion 15 c, and the shaft portion 15 d. The base portion 15 b is overlapped on the inside of the lid 11 b as the battery case component, with an insulating member (the gasket 12) interposed between the base portion 15 b and the lid 11 b. The seat portion 15 c protrudes from the base portion 15 b. The seat portion 15 c is inserted through the mounting hole 11 c and fitted to the lid 11 b with insulating members (12, 13) interposed between them. The shaft portion 15 d rises at a central part of the seat portion 15 c. The external terminal 14 includes the insertion hole 14 c and the welded portion 14 d. The insertion hole 14 c is a hole through which the shaft portion 15 d of the internal terminal 15 is to be inserted. The welded portion 14 d is a portion of the external terminal 14 that is overlapped on the seat portion 15 c in the region around the insertion hole 14 c and is welded to the internal terminal 15. Further, the shaft portion 15 d of the internal terminal 15 is fastened to the external terminal 14.

In this battery 10, the external terminal 14 includes the welded portion 14 d welded to the internal terminal 15 in the portion of the external terminal 14 that overlaps the seat portion 15 c within the region around the insertion hole 14 c. The welded portion 14 d is formed on the back side of the external terminal 14, which means that the welded portion 14 d is not exposed on the surface. As a result, extraneous matters do not easily come into contact with the welded portion 14 d from outside, so it is easy to maintain the quality of the conductive path at high level. Moreover, the shaft portion 15 d of the internal terminal 15 is fastened to the external terminal 14 in this embodiment. In other words, the internal terminal 15 is fastened to the external terminal 14 like a rivet. Therefore, it is easy to maintain the internal terminal 15 in such a state that the internal terminal 15 is fitted to the lid 11 b, the gasket 12, the insulator 13, and the external terminal 14. As a result, even when an external force acts on the battery 10 such as to pull the welded portion 14 d apart, the joint between the internal terminal 15 and the external terminal 14 is maintained by the welded portion 14 d. Although not shown in the drawings, it is also possible that the outer circumferential edge of the shaft portion 15 d of the internal terminal 15 that has been fastened to the external terminal 14 may be additionally welded to the external terminal 14 by, for example, laser welding. The welding in this manner joins the internal terminal 15 and external terminal 14 more firmly to each other. Furthermore, the reliability of the conductive path between the internal terminal 15 and the external terminal 14 is improved because the conductive path is formed on both the inside and the outside of the internal terminal 15 and the external terminal 14, although the manufacturing cost may be increased thereby.

In this embodiment, the external terminal 14 is welded to the internal terminal 15 by the welded portion 14 d, which is provided on the back surface of the external terminal 14. This welded portion 14 d shows low electrical resistance because the surface films of the internal terminal 15 and the external terminal 14 are melted therein, which means that the welded portion 14 d may serve as a conductive path. This may shorten the conductive path between the internal terminal 15 and the external terminal 14 in comparison with conventional cases where the tip end of the shaft portion 15 d of the internal terminal 15 is fastened to the region around the insertion hole 14 c of the external terminal 14 and the circumferential edge of the fastened shaft portion 15 d of the internal terminal 15 is welded to the external terminal 14. As a result, the structure in which the external terminal 14 is joined to the internal terminal 15 by the welded portion 14 d provided on the back surface of the external terminal 14 may also contribute to reducing the battery resistance in the battery 10.

The following describes a method of manufacturing the above-described battery 10 and a welding method of the above-described welded portion 14 d.

The method of manufacturing the battery 10 includes a step of preparing a battery case component (the lid 11 b herein), a step of preparing the gasket 12, a step of preparing the internal terminal 15, a step of preparing the insulator 13, a step of preparing the external terminal 14, an assembling step, a welding step, and a fastening step.

FIG. 3 is a cross-sectional view illustrating the internal terminal 15, the gasket 12, the lid 11 b, the insulator 13, and the external terminal 14 that are assembled together in the assembling step. FIG. 4 is a plan view illustrating a region surrounding the insertion hole 14 c of the external terminal 14 in the assembling step. FIG. 5 is a cross-sectional view illustrating how the external terminal 14 is pressed against the seat portion 15 c of the internal terminal 15 in the welding step. FIG. 6 is a partial cross-sectional view taken along line VI-VI in FIG. 5 . FIG. 6 shows a region surrounding the insertion hole 14 c of the external terminal 14 in the welding step. FIGS. 3 and 5 show a cross section of the lid 11 b along its longitudinal axis.

The lid 11 b, serving as a battery case component prepared herein, may preferably be formed with a mounting hole 11 c, as already described. The gasket 12 prepared here may preferably include the tubular portion 12 a attachable to the mounting hole 11 c, as already described. The internal terminal 15 prepared here may preferably include the seat portion 15 c attachable to the tubular portion 12 a and the shaft portion 15 d rising at a central portion of the seat portion 15 c, as already described. The insulator 13 prepared here includes the protrusion 13 e and the through hole 13 d to be fitted with the seat portion 15 c. The external terminal 14 prepared here includes the insertion hole 14 c through which the shaft portion 15 d is to be inserted and the through hole 14 e. Here, the protrusion 13 e of the insulator 13 is provided in a vicinity of the through hole 13 d, which is to be attached to the seat portion 15 c. The through hole 14 e of the external terminal 14 is formed corresponding to the position at which the protrusion 13 e is provided. In this embodiment, the insulator 13 is provided with two protrusions 13 e so as to sandwich the through hole 13 d to be attached to the seat portion 15 c along the longitudinal axis of the lid 11 b. The external terminal 14 is formed with through holes 14 e, the positions of which are adjusted so that the protrusions 13 e can protrude therefrom.

In the assembling step, the internal terminal 15, the gasket 12, the lid 11 b, the insulator 13, and the external terminal 14 are assembled together, as illustrated in FIG. 3 . In the assembling step, for example, the tubular portion 12 a of the gasket 12 is fitted onto the mounting hole 11 c of the lid 11 b, serving as a battery case component. The seat portion 15 c of the internal terminal 15 is fitted into the tubular portion 12 a of the gasket 12. The insulator 13 is disposed on the outer surface of the lid 11 b while attaching the seat portion 15 c to the through hole 13 d. Further, when arranging the external terminal 14 on the insulator 13, the shaft portion 15 d of the internal terminal 15 is inserted through the insertion hole 14 c, and the protrusions 13 e of the insulator 13 are inserted into the through holes 14 e of the external terminal 14. Note that the procedure of assembling the internal terminal 15, the gasket 12, the lid 11 b, the insulator 13, and the external terminal 14 in the assembling step is not limited to the one described above. For example, in the assembling step, it is also possible that the gasket 12, the lid 11 b, the insulator 13, and the external terminal 14 may be fitted onto the internal terminal 15 in that order.

In the welding step, as illustrated in FIG. 5 , for example, the internal terminal 15 and the external terminal 14 that are assembled together in the assembling step as described above are clamped by a horn 41 and an anvil 42 (supporting jig). In this embodiment, the horn 41 is put onto the upper surface of the external terminal 14, and the anvil 42 is put onto the lower surface of the base portion 15 b of the internal terminal 15. Then, the external terminal 14 is pressed against the seat portion 15 c of the internal terminal 15. As illustrated in FIG. 6 , the horn 41 is pressed against four locations on the external terminal 14 around a region surrounding the insertion hole 14 c through which the shaft portion 15 d is inserted. The tip ends of the horn 41 are circumferentially uniformly arranged. In this embodiment, each of the edge faces of the horn 41 is in a rectangular shape. However, the horn 41 may have an edge face in a circular arc shape along the circumference around the region surrounding the insertion hole 14 c, through which the shaft portion 15 d is inserted.

The horn 41 is mounted to a press 41 a equipped with a vibration generator. The vibration generator is a device that applies vibrations required for ultrasonic welding to the horn 41. The vibration generator may preferably incorporate, for example, a transducer or a booster. The anvil 42 is mounted so as to oppose the horn 41. In this embodiment, the anvil 42 is put onto the base portion 15 b of the internal terminal 15 at a position opposite to the horn 41.

Further, as illustrated in FIG. 5 , the protrusions 13 e inserted through the through holes 14 e of the external terminal 14 are pressed down, whereby the insulator 13 is elasticity deformed. This causes the insulator 13 to be detached from the external terminal 14 in a region surrounding the seat portion 15 c. Each of the protrusions 13 e may preferably be pressed down by, for example, a pressing member 44 of the press 44 a. Whether the insulator 13 is detached from the external terminal 14 in the region surrounding the seat portion 15 c may be determined by the reaction force that acts on the pressing member 44 of the press 44 a.

When the external terminal 14 is pressed against the seat portion 15 c of the internal terminal 15, the internal terminal 15, the gasket 12, the lid 11 b, the insulator 13, and the external terminal 14 are brought into intimate contact with each other. In addition, in this embodiment, the protrusion 11 c 1 provided at the rim of the mounting hole 11 c of the lid 11 b bites into the gasket 12.

Whether or not the external terminal 14 is sufficiently pressed against the seat portion 15 c of the internal terminal 15 is determined from the clamping force exerted by the horn 41 and the anvil 42. For example, if the necessary compression load is about 2000 N, the clamping force exerted by the pressing member 44, the horn 41, and the anvil 42 of the press 44 a may be set to 2000 N. The clamping force exerted by the pressing member 44, the horn 41, and the anvil 42 may be controlled to 2000 N by, for example, measuring the reaction force acting on the member that supports the anvil. This guarantees the internal terminal 15 and the external terminal 14 to be pressed against each other so that they are brought into intimate contact with each other on the seat portion 15 c, and also guarantees the protrusion 11 c 1 provided at the rim of the mounting hole 11 c of the lid 11 b to bite into the gasket 12.

Next, as described above, the pressing member 44 of the press 44 a detaches the insulator 13 from the external terminal 14 in the region surrounding the seat portion 15 c, and the horn 41 applies ultrasonic vibration to the external terminal 14 while pressing the external terminal 14 against the seat portion 15 c of the internal terminal 15. As a result, the external terminal 14 and the seat portion 15 c of the internal terminal 15, which are pressed against each other by being clamped by the horn 41 and the anvil 42 (supporting jig), are welded to each other. In this case, because the insulator 13 is detached from the external terminal 14 in the region surrounding the seat portion 15 c as described above, the vibration transmitted from the horn 41 to the external terminal 14 is easily transmitted directly to the contact points between the external terminal 14 and the seat portion 15 c of the internal terminal 15. Accordingly, within the external terminal 14 and the seat portion 15 c of the internal terminal 15, the position that is clamped by the horn 41 and the anvil 42 (supporting jig) and is directly affected by the pressing force is welded. Thus, in the welding step, ultrasonic vibration may be applied to the internal terminal 15 or the external terminal 14 while detaching the insulator 13 from the external terminal 14 in at least the region surrounding the seat portion 15 c and pressing the external terminal 14 and the seat portion 15 c of the internal terminal 15 against each other.

Here, while checking the level of the pressing force applied from the horn 41 to the external terminal 14, ultrasonic vibration is applied to the horn 41 with a predetermined pressing force being applied to the external terminal 14. Then, the external terminal 14 is vibrated under the conditions where the internal terminal 15, the gasket 12, the lid 11 b, the insulator 13, and the external terminal 14 are in intimate contact with each other and where the protrusion 11 c 1 provided at the rim of the mounting hole 11 c of the lid 11 b bites into the gasket 12. In this case, the internal terminal 15 pressed by the anvil 42 is fixed, and the external terminal 14 pressed by the horn 41 vibrates in synchronization with the horn 41. The vibration applied through the horn 41 to the external terminal 14 may preferably have a frequency such that the internal terminal 15 and the external terminal 14 can be solid-state welded. From this viewpoint, it is desirable that the vibration applied through the horn 41 to the external terminal 14 be, for example, from about 20 kHz to about 100 kHz.

In addition, it is desirable that the horn 41 be vibrated, for example, circumferentially about the center axis of the shaft portion 15 d of the internal terminal 15. This ultrasonic vibration causes the joint interface between the external terminal 14 and the seat portion 15 c of the internal terminal 15 to be solid-state welded. In other words, the internal terminal 15 and the external terminal 14 are welded together at a temperature lower than their melting temperature.

As a result, the external terminal 14 and the seat portion 15 c of the internal terminal 15 should be welded, for example, around the shaft portion 15 d of the internal terminal 15 along a circumferential direction. In other words, the welded portion 14 d may be in a circular arcuate shape. In addition, the welded portion 14 d should desirably have a certain area in order to obtain required strength. For example, the welded portion 14 d may have an area of equal to or greater than 20 mm² (e.g., 30 mm²).

In this embodiment, vibration is applied to the external terminal 14 through the horn 41, but this is merely illustrative. For example, although not shown in the drawings, it is also possible that the external terminal 14 may be held by an anvil, and a horn may be attached to the internal terminal 15, so that vibration can be applied through the horn to the internal terminal 15.

Thus, in the welding step, the seat portion 15 c and the external terminal 14 are solid-state welded together by causing the external terminal 14 or the internal terminal 15 to vibrate while detaching the insulator 13 from the external terminal 14 in at least a region surrounding the seat portion 15 c and pressing the external terminal 14 against the seat portion 15 c of the internal terminal 15. The solid-state welding in this manner produces atomic level bonding between the external terminal 14 and the internal terminal 15 and provides sufficient electrical conductivity between the external terminal 14 and the internal terminal 15 at low resistance. In the welding step of this method, the insulator 13 is detached from the external terminal 14 in at least the region surrounding the seat portion 15 c. Therefore, this method enables the external terminal 14 to be reliably pressed against the seat portion 15 c of the internal terminal 15 when vibrating the external terminal 14 or the internal terminal 15. Because the insulator 13 is detached from the external terminal 14 in the region surrounding the seat portion 15 c, the insulator 13 is unlikely to hinder the vibration, so the seat portion 15 c and the external terminal 14 are solid-state welded at high quality.

FIG. 7 is a cross-sectional view illustrating the fastening step. In the fastening step, as illustrated in FIG. 7 , the shaft portion 15 d is fastened to a region around the insertion hole 14 c of the external terminal 14 after the welding step. In this embodiment, as illustrated in FIG. 7 , the horn 41, which has been used in the welding step, is removed, and a riveting tool member 43 is pressed against the tip end 15 d 1 of the shaft portion 15 d of the internal terminal 15. The riveting tool member 43 is mounted to an actuator 43 a, such as a servomotor, in such a manner that it is pressed against the tip end 15 d 1 of the shaft portion 15 d of the internal terminal 15 as it rotates. In this fastening step as well, the insulator 13 may be detached from the external terminal 14 in at least a region surrounding the seat portion 15 c. Then, after the fastening step, the insulator 13 may be released from being detached from the external terminal 14 in at least the region surrounding the seat portion 15 c. More specifically, in the fastening step as well, the insulator 13 may be detached from the external terminal 14 in the region surrounding the seat portion 15 c by the pressing member 44 of the press 44 a. Then, after the fastening step, the pressing member 44 of the press 44 a may be removed from the protrusion 13 e of the insulator 13. Then, the pressing member 44 of the press 44 a may release the protrusion 13 e of the insulator 13 that has been pressed down by the pressing member 44.

Since the insulator 13 is detached from the external terminal 14 in at least the region surrounding the seat portion 15 c in the fastening step in this way, the welded portion 14 d produced in the welding step is not easily affected by the reaction force from the insulator 13. Then, under this condition, the tip end 15 d 1 of the shaft portion 15 d of the internal terminal 15 is fastened to the region around the insertion hole 14 c of the external terminal 14. As a result, the welded portion 14 d produced in the welding step is maintained appropriately.

Although it is depicted schematically in FIG. 7 , the fastening step may involve compressing and deforming the tip end 15 d 1 of the shaft portion 15 d of the internal terminal 15 with a rotatable riveting tool member 43. After the fastening step, the pressing member 44 of the press 44 a may be removed from the protrusion 13 e. When the pressing member 44 of the press 44 a is removed from the protrusion 13 e, the insulator 13, the protrusions 13 e of which have been pressed down, is caused to return to its original shape in the region surrounding the seat portion 15 c, as illustrated in FIG. 2 . This causes the insulator 13 to be sandwiched between the lid 11 b and the external terminal 14.

In addition to the above-described solid-state welding, it is possible that the outer circumferential edge of the fastened shaft portion 15 d of the internal terminal 15 may be additionally welded to the external terminal 14. This welding allows the internal terminal 15 and the external terminal 14 to be joined more firmly to each other. When the outer circumferential edge of the shaft portion 15 d of the internal terminal 15 is additionally welded to the external terminal 14, the external terminal 14 and the internal terminal 15 are bonded at the atomic level in a greater region, so the electrical conductivity between the external terminal 14 and the internal terminal 15 can be further improved. The welding of the outer circumferential edge of the fastened shaft portion 15 d of the internal terminal 15 may be carried out by laser welding.

Although embodiments of the battery 10, the manufacturing method of the battery 10, and the welding method of the welded portion 14 d have been described hereinabove, the battery 10, the manufacturing method of the battery 10, and the welding method of the welded portion 14 d are not limited to the embodiments described above.

Here, FIG. 8 is a cross-sectional view illustrating a battery according to another embodiment of the disclosure. FIG. 8 shows a portion of the battery in which an external terminal 14 and an internal terminal 15 are fitted to a battery case 11. In the embodiment shown in FIG. 8 , the external terminal 14 includes a through hole 14 e in a vicinity of the portion of the external terminal 14 that overlaps the seat portion 15 c. The insulator 13 includes a protrusion 13 e protruding into the through hole 14 e. In this embodiment, the protrusion 13 e protrudes into the through hole 14 e, but it does not protrude from the through hole 14 e. As illustrated in FIG. 8 , the protrusion 13 e of the insulator 13 may protrude to an intermediate portion of the through hole 14 e, or may protrude to a position such as not to protrude from the through hole 14 e. In the welding step, a rod or the like may be inserted into the through hole 14 e to press down the protrusion 13 e. Thereby, the insulator 13 is detached from the external terminal 14 in a region surrounding the seat portion 15 c of the internal terminal 15. Therefore, in the welding step in which the seat portion 15 c and the external terminal 14 are solid-state welded to each other by causing the external terminal 14 or internal terminal 15 to vibrate, the insulator 13 is unlikely to hinder the vibration produced in the external terminal 14 or the internal terminal 15. As in the embodiment shown in FIG. 2 , the seat portion 15 c and the external terminal 14 are solid-state welded to each other more reliably.

FIG. 9 is a cross-sectional view illustrating a battery according to still another embodiment of the disclosure. In the embodiment shown in FIG. 9 , the external terminal 14 includes a through hole 14 e in a vicinity of the portion of the external terminal 14 that overlaps the seat portion 15 c. In this embodiment, the protrusion 13 e (see FIGS. 2 and 8 ) that protrudes into the through hole 14 e is eliminated from the insulator 13. In the welding step, a rod or the like may be inserted into the through hole 14 e to press down the insulator 13. Thereby, the insulator 13 is detached from the external terminal 14 in a region surrounding the seat portion 15 c of the internal terminal 15. Therefore, in the welding step in which the seat portion 15 c and the external terminal 14 are solid-state welded to each other by causing the external terminal 14 or internal terminal 15 to vibrate, the insulator 13 is unlikely to hinder the vibration produced in the external terminal 14 or the internal terminal 15. As in the embodiment shown in FIG. 2 , the seat portion 15 c and the external terminal 14 are solid-state welded to each other more reliably.

FIG. 10 is a cross-sectional view illustrating a battery according to yet another embodiment of the disclosure. In the embodiment shown in FIG. 10 , the external terminal 14 includes a thinned portion 14 f in a region surrounding a portion of the external terminal 14 that overlaps the seat portion 15 c. Referring to FIG. 10 , the external terminal 14 is formed with holes 14 g in a vicinity of the portion of the external terminal 14 that overlaps the seat portion 15 c, and a thinned portion 14 f is provided at the bottom portion of each of the holes 14 g. Provision of the thinned portion 14 f enables the welded portion 14 d to be isolated from the air and to provide a sufficient distance between the welded portion 14 d and the air. Provision of the thinned portion 14 f prevents water or extraneous matters from entering between the external terminal 14 and the insulator 13. As a result, it is easy to maintain the quality of the solid-state welding at high level. It is desirable that the thinned portion 14 f be designed to have a strength such that it is not punctured when pressed down by a rod. It is desirable to provide a thinner portion at a central portion of the thinned portion 14 f and a thicker portion around the central portion. In other words, the thinned portion 14 f may be designed so that its thickness reduces gradually toward the central portion.

In this embodiment, it is desirable that in the welding step, a rod or the like be inserted into the hole 14 g provided with the thinned portion 14 f so that the insulator 13 is pressed down. Thereby, the insulator 13 is detached from the external terminal 14 in a region surrounding the seat portion 15 c of the internal terminal 15. Therefore, in the welding step in which the seat portion 15 c and the external terminal 14 are solid-state welded to each other by causing the external terminal 14 or internal terminal 15 to vibrate, the insulator 13 is unlikely to hinder the vibration produced in the external terminal 14 or the internal terminal 15. As in the embodiment shown in FIG. 2 , the seat portion 15 c and the external terminal 14 are solid-state welded to each other more reliably.

FIG. 11 is a cross-sectional view illustrating a welding step of a battery according to further another embodiment of the disclosure. FIG. 12 is a plan view of an internal terminal 15, illustrating how an insulator 13 is fitted to a seat portion 15 c of the internal terminal 15 in an assembling step of the battery of the embodiment shown in FIG. 11 .

For example, as illustrated in FIGS. 11 and 12 , the welded portion 14 d, at which the external terminal 14 is welded to the internal terminal 15, may be provided radially outward relative to the portion of the shaft portion 15 d that is fastened to the region around the insertion hole 14 c of the external terminal 14 (in other words, radially outward relative to the shaft portion 15 d). In the embodiment shown in FIGS. 11 and 12 , the seat portion 15 c of the internal terminal 15 is in an elliptic shape the major axis of which is set along the longitudinal axis of the lid 11 b. In addition, the seat portion 15 c of the internal terminal 15, to which the external terminal 14 is to be joined, is provided with grooves 15 c 1. In the welding step, the horn 41 is placed onto two points that are spaced part along the major axis of the seat portion 15 c of the internal terminal 15, for example, as illustrated in FIG. 11 . With respect to the major axis of the seat portion 15 c of the internal terminal 15, each of the grooves 15 c 1 is formed inward relative to the positions on which the horn 41 is to be placed. Furthermore, through holes 14 e are formed in the external terminal 14. With respect to the major axis of the seat portion 15 c of the internal terminal 15, the through holes 14 e are formed outward relative to the positions on which the horn 41 is placed. The insulator 13 is provided with protrusions 13 e protruding into the through holes 14 e.

In the welding step of this embodiment, the protrusions 13 e should be pressed down so that the insulator 13 is detached from the external terminal 14 in the region surrounding the seat portion 15 c. In particular, the insulator 13 should be pressed down and detached from the external terminal 14 in a vicinity directly below the position on which the horn 41 is to be placed. Then, while the insulator 13 is detached from the external terminal 14 in the region surrounding the seat portion 15 c, the horn 41 may cause the external terminal 14 to be pressed against the internal terminal 15, and may also apply ultrasonic vibration to the external terminal 14. Thus, the external terminal 14 and the internal terminal 15 are solid-state welded to each other in a region where the external terminal 14 is pressed against the internal terminal 15 by the horn 41. Thereafter, although not shown in the drawings, the protrusions 13 e are pressed down and the insulator 13 is detached from the external terminal 14 in the region surrounding the seat portion 15 c. Then, while the insulator 13 is detached from the external terminal 14 in the region surrounding the seat portion 15 c, the shaft portion 15 d of the internal terminal 15 may be fastened to a region around the insertion hole 14 c of the external terminal 14.

In this embodiment, the grooves 15 c 1 are formed in the seat portion 15 c of the internal terminal 15 to which the external terminal 14 is to be joined. When fitting the external terminal 14 onto the seat portion 15 c, it is possible that extraneous matters may be caught between the seat portion 15 c and the external terminal 14. When this occurs, the grooves 15 c 1 formed in the seat portion 15 c allow the extraneous matters to fall into the grooves 15 c 1. This further enhances the reliability of welding of the seat portion 15 c and the external terminal 14. As illustrated in FIG. 11 , for example, the groove 15 c 1 may be provided inward relative to the position at which the external terminal 14 is pressed by the horn 41, with respect to the radial axis of the shaft portion 15 d of the internal terminal 15. That is, it is desirable that, with respect to the radial axis of the shaft portion 15 d, the groove 15 c 1 be formed at a position in the seat portion 15 c that is closer to the shaft portion 15 d than the welded portion 14 d, at which the external terminal 14 is welded to the seat portion 15 c of the internal terminal 15. In other words, it is desirable that the groove 15 c 1 be formed at a position in the seat portion 15 c that is close to the insertion hole 14 c of the external terminal 14, through which the shaft portion 15 d is inserted.

It is desirable that each of the grooves 15 c 1 in the seat portion 15 c be formed so that an extraneous matter with a size of about 50 μm to about 200 μm can fall therein when the external terminal 14 is fitted to the seat portion 15 c. From this viewpoint, it is desirable that each of the grooves 15 c 1 have a depth of from about 200 μm to about 500 μm. From this viewpoint, it is desirable that each of the grooves 15 c 1 have a width of from about 200 μm to about 2 mm. In the example of FIG. 12 , each of the grooves 15 c 1 is formed in a straight line shape. However, the shape of the groove 15 c 1 is not limited to any particular shape.

Although this embodiment shows that the fastening step is performed after the welding step, it is also possible that the fastening step may be performed during the welding step. Specifically, it is possible to place a riveting tool member onto the shaft portion 15 d of the internal terminal 15 and fasten the shaft portion 15 d of the internal terminal 15 to a region around the insertion hole 14 c of the external terminal 14 while the horn 41 is pressing the external terminal 14 against the internal terminal 15 and is applying ultrasonic vibration to the external terminal 14.

FIG. 13 is a cross-sectional view illustrating another embodiment of the battery according to the present disclosure. In the embodiment shown in FIG. 13 , the external terminal 14 is overlapped and welded to the seat portion 15 c of the internal terminal 15. The seat portion 15 c provided here is inserted through the mounting hole 11 c and fitted into the lid 11 b (battery case component) with the gasket 12 and the insulator 13, serving as the insulating members, being interposed between the seat portion 15 c and the lid 11 b. The external terminal 14 overlaps the seat portion 15 c inserted through the mounting hole 11 c and includes the welded portion 14 d welded to the internal terminal 15 in the portion of the external terminal 14 that overlaps the seat portion 15 c.

In the embodiment shown in FIG. 13 , the tubular portion 12 a of the gasket 12 is fitted to the mounting hole 11 c of the lid 11 b in the assembling step of assembling together the internal terminal 15, the gasket 12, the lid 11 b, the insulator 13, and the external terminal 14. The seat portion 15 c of the internal terminal 15 is fitted into the tubular portion 12 a of the gasket 12. The insulator 13 is disposed on the outer surface of the lid 11 b while fitting the seat portion 15 c to the through hole 13 d. The external terminal 14 is disposed so as to overlap the seat portion 15 c above the insulator 13.

As illustrated in FIG. 13 , the external terminal 14 includes through holes 14 e in a vicinity of the portion of the external terminal 14 that overlaps the seat portion 15 c. The insulator 13 is provided with protrusions 13 e that protrude into through holes 14 e. Although not shown in the drawings, each of the protrusions 13 e may be pressed down by the pressing member 44 of the press 44 a in the welding step. Thereby, the insulator 13 is detached from the external terminal 14 in a region surrounding the seat portion 15 c of the internal terminal 15. Moreover, in the welding step in which the seat portion 15 c and the external terminal 14 are solid-state welded to each other by causing the external terminal 14 or internal terminal 15 to vibrate, the insulator 13 is unlikely to hinder the vibration produced in the external terminal 14 or the internal terminal 15.

In the embodiment shown in FIG. 13 , the external terminal 14 is overlapped over a wide area of the seat portion 15 c. As a result, the internal terminal 15 and the external terminal 14 are solid-state welded over a wide area. The solid-state welding should desirably be carried out by pressing a horn against the external terminal 14 and pressing an anvil against the base portion 15 b of the internal terminal 15 at the position corresponding to the horn. Then, the external terminal 14 may be pressed against the seat portion 15 c of the internal terminal 15 by the horn and the anvil, and the external terminal 14 may be caused to vibrate by the horn. In the battery according to the embodiment shown in FIG. 13 , the internal terminal 15 and the external terminal 14 are solid-state welded over a wide area, and by the solid-state welded portion 14 d, the internal terminal 15 and the external terminal 14 are joined at a required strength.

That is, the shaft portion 15 d (see FIG. 2 ) is eliminated from the seat portion 15 c. Also, the insertion hole 14 c (see FIG. 2 ) through which the shaft portion 15 d is to be inserted is eliminated from the external terminal 14. This is different from the embodiment in which the shaft portion 15 d is fastened to a region surrounding the insertion hole 14 c of the external terminal 14. However, the external terminal 14 is welded to a wide area of the seat portion 15 c of the internal terminal 15, whereby the external terminal 14 and the internal terminal 15 are welded to each other at a required strength.

It is also possible that the upper surface of the seat portion 15 c may be provided with a groove (see FIG. 11 ) for allowing extraneous matters to fall therein at an appropriate position, although it is not employed in the example shown in FIG. 13 .

As has been discussed above, the battery 10 proposed herein embodies welding the internal terminal 15 and the external terminal 14 to each other, without use of laser welding, in the welding step for providing a conductive path between the internal terminal 15 and the external terminal 14. Moreover, the conductive path between the internal terminal 15 and the external terminal 14 is formed in a contact portion between the internal terminal 15 and the external terminal 14 that is not exposed outside. This makes it possible to maintain the quality of the conductive path between the internal terminal 15 and the external terminal 14 at high level. Furthermore, the equipment cost can be reduced because the welding step for forming the conductive path between the internal terminal and the external terminal uses a solid-state welding machine, which is relatively less costly than a laser welding machine.

Various embodiments of the battery and the method of manufacturing a battery module have been described hereinabove according to the present disclosure. Unless specifically stated otherwise, the embodiments of the battery and the method of manufacturing the battery described herein do not limit the scope of the present invention.

For example, unless otherwise stated, the structure of the battery case and that of the electrode assembly are not limited to those described in the foregoing embodiments.

For example, in the foregoing embodiments, the internal terminal 15 and the external terminal 14 are mounted to the lid 11 b, which is a battery case component. However, depending on the structure of the battery case, this is not necessarily the case. In other words, the battery case component is not limited to the lid. It is possible that the internal terminal 15 and the external terminal 14 may be mounted to the case main body in which the electrode assembly is enclosed. In that case, the case main body may be the battery case component. Although the foregoing embodiments show the gasket 12 and the insulator 13 as examples of the insulating member, the insulating member is not limited thereto and may be interposed between the internal terminal 15 and a battery case component and between the external terminal 14 and the battery case component. 

What is claimed is:
 1. A battery comprising: a battery case component including a mounting hole; an internal terminal; an external terminal; and an insulating member interposed between the battery case component and the internal terminal and between the battery case component and the external terminal, wherein: the internal terminal includes a base portion and a seat portion protruding from the base portion, the base portion being overlapped on an inside of the battery case component with the insulating member being interposed between the base portion and the inside of the battery case component, and the seat portion inserted through the mounting hole with the insulating member being interposed between the seat portion and the mounting hole and attached to the battery case component; and the external terminal includes a welded portion and a through hole, the welded portion being overlapped on the seat portion inserted through the mounting hole and being welded to the internal terminal, and the through hole formed in a vicinity of a part of the external terminal that overlaps the seat portion.
 2. The battery according to claim 1, wherein the insulating member includes a protrusion protruding into the through hole.
 3. The battery according to claim 1, wherein: the internal terminal further includes a shaft portion rising from the seat portion; the external terminal further includes an insertion hole through which the shaft portion is inserted; and the shaft portion is inserted through the insertion hole and fastened to a region around the insertion hole.
 4. A battery comprising: a battery case component including a mounting hole; an internal terminal; an external terminal; and an insulating member interposed between the battery case component and the internal terminal and between the battery case component and the external terminal, wherein: the internal terminal includes a base portion and a seat portion protruding from the base portion, the base portion being overlapped on an inside of the battery case component with the insulating member being interposed between the base portion and the inside of the battery case component, and the seat portion inserted through the mounting hole with the insulating member being interposed between the seat portion and the mounting hole and attached to the battery case component; and the external terminal includes a welded portion and a thinned portion, the welded portion being overlapped on the seat portion inserted through the mounting hole and being welded to the internal terminal, and the thinned portion having a reduced thickness and provided in a vicinity of a portion of the external terminal that overlaps the seat portion.
 5. The battery according to claim 4, wherein: the internal terminal further includes a shaft portion rising from the seat portion; the external terminal further includes an insertion hole through which the shaft portion is inserted; and the shaft portion is inserted through the insertion hole and fastened to a region around the insertion hole. 